This invention relates generally to fittings or couplings, and more particularly to improvements in tube fitting union nuts and nut assemblies.
When tightening tube fitting or coupling union nuts, severe twisting stresses are imparted to the tubes. When exposed to any transient vibrations, these fittings will have a tendency to loosen. One method to eliminate this stress is to reduce the friction of the threads by means of silver plating. Also accurate initial alignment of the tubes is required to allow the nut threads to be started, and to prevent any distortion of interengaging tube parts when the union is tightened. Current tube fitting union nuts do not adequately assure such tube alignment, and the tubes can loosen when vibrated.
There is need for an improved fitting or coupling assembly that will eliminate or substantially reduce twisting forces imparted to tube parts during coupling or fitting make-up, without reducing the ultimate tightening force of the union; also, there is need for improvements in such fittings that will assure adequate axial alignment of the tubular parts to be interconnected. There is particular need in this regard, as respects tubular parts having end flanges, with opposed annular protrusions that engage opposite faces of a sealing washer, as will appear.